Honestly, what I never understood was that years after GM introduced the LS-series engines, they never decided to create a V6 version by cutting off 2 cylinders, as they did with the 4.3 V6.
I think the #1 reason engine architectures get cancelled is smog. Sometimes to pass smog, an engine's entire architecture might have to be changed. Ever read the documentary about how Chrysler made the AMC 258 into the Jeep 4.0? The engine had to be redesigned for a wider bore to help compensate for a shorter stroke. The cylinder heads also had to be completely different. That might not be economical in all situations. Other times, an old engine design can pass smog, but only by adding an air pump, precats, EGR, a compromised cam profile, and more stuff. Having all that extra stuff might be more expensive than an engine that creates low smog right from the combustion chamber. Next, there would be the concern that the way the engine handles heat would be a problem, as uniform temperatures are important to prevent HC from the cold places and NOx from the high places. Some engines now have multiple coolant pats in the cylinder head and block to improve this.
Combustion chamber design may have hurt the possibility of a newer 3800. Wedge OHV engines are cheaper to build than canted and Hemi OHV heads, would it be too expensive to replace the wedge heads of the 3800 with canted valve heads? Would the shape of the lifter valley and the height of the lifter to the rocker arm be too high to allow changing pushrod geometry?
Another thing the 3800 faced was the price of superchargers. They typically cost more than turbos, and they might both be more expensive than a new DOHC engine.
In some countries, cars are taxed by engine displacement. In those cases, having a dense HP/L is critical to the success of a car. Selling one engine to North America, and a different engine to Europe might not be the most cost effective idea.
I like the GM 3800 engine, but I can see why it may have been eliminated.
Also, some of GM's DOHC engines used during the production of the 3800 weren't all that great. People tell me they don't miss the 3.4 DOHC that GM used in the 1990s Chevy Lumina which wasn't much more powerful than a later generation 3800. Making a DOHC engine may have been considered too much of a risk.